Discontinuous reception allows a user equipment (UE) to turn off its radio transceiver during various periods in order to save battery life on the UE. In the long term evolution (LTE) specifications, the UE is allowed to proceed into discontinuous reception (DRX) even when in a connected mode. DRX operation is defined for single carrier operation in LTE Release 8, in 3GPP TS 36.321, sections 3.1 and 5.7, the contents of which are incorporated herein by reference.
In LTE Advanced (LTE-A) it is agreed that carrier aggregation may be used in order to support a wider transmission bandwidth for increased potential peak data rates to meet the LTE-A requirements. In carrier aggregation, multiple component carriers are aggregated and they can be allocated in a subframe to a UE. Thus, each component carrier may have a bandwidth of, for example, 20 MHz and a total aggregated system bandwidth of up to 100 MHz. The UE may receive or transmit on multiple component carriers depending on its capabilities. Further, carrier aggregation may occur with carriers located in the same band and/or carriers located in different bands. For example, one carrier may be located at 2 GHz and a second aggregated carrier may be located at 800 MHz.
An issue arises with the translation of DRX operation from a single carrier LTE Rel-8 system to a multiple carrier LTE-A system. DRX under LTE Rel-8 may be inoperable or inefficient when multiple carriers are used. Two approaches have been proposed at the LTE-A forum.
In R2-092959, “DRX with Carrier Aggregation in LTE-Advanced”, a proposal is described in which different DRX parameters are configured independently for different component carriers and DRX is performed independently for each component carrier. For example, one component carrier may utilize a short DRX cycle while another component carrier may utilize only long DRX cycles; or the DRX cycles configured for the different component carriers are completely independent of one another. A problem with this approach is the complexity for the UE to maintain different states or timers for different carriers. There may also be little benefit of having completely independent DRX cycles and timers between carriers. Since upper layer traffic is multiplexed across multiple carriers, it is the Evolved Node B (eNB) scheduler's decision to determine on which carrier an encoded packet should be transmitted.
In a second approach, outlined in R2-092992, “Consideration on DRX”, DRX operation is only configured on the anchor carrier. Additional component carriers are allocated on an as needed basis during the “active time” of the anchor carrier.
However, the above two proposals do not provide details regarding the allocation and de-allocation of additional component carriers. Nor do they explicitly provide details as to the DRX operation of the various carriers.